A complete sequence was obtained for the 6578-nucleotide L gene, the 155-nucleotide 5'-trailer region and the 44-nucleotide leader region of RSV genomic RNA (vRNA) of strain A2 of subgroup A. This completes the sequence analysis of the 15,222-nucleotide RSV vRNA. cDNAs have been constructed for the in vitro syntheses of synthetic vRNA-like molecules. These "vRNAs" contain a marker gene (chloramphenicol acetyltransferase) under the control of RSV transcriptive signals and flanked by the RSV 3' and 5' vRNA sequences that are thought to contain promoters that direct transcription and replication. We are exploring methods for introducing these synthetic vRNAs into RSV-infected cells such that they will associate with viral proteins and be transcribed and replicated.